FAQ:
Why is the exp per hour low?
The minigame requires you to click constantly in order to maximise exp, and it's hard to do that more efficiently with RuneMate. I've spent many hours optimising the bot, and have almost certainly tried any obvious suggestions that you have.

Why not plant more than 8 at a time?
The extra time taken results in plants dying before being watered. Since the last 25 plants give double exp, it's more efficient to guarantee that the plants live rather than planting more at one time.